Apparatus for making high-sensitivity measurements of various parameters, and sensors particularly useful in such apparatus

ABSTRACT

A sensor for sensing a predetermined parameter having a known relationship with respect to the transit time of an energy wave through a medium, includes a body of soft elastomeric material having high transmissivity and low attenuation properties with respect to the energy waves; and a transmitter and receiver carried by the body in spaced relation to each other such that the energy waves received by the receiver are those transmitted by the transmitter after having traversed at least a portion of the body of soft elastomeric material. The transit time of the energy wave through the elastomeric body is measured to produce a measurement of the predetermined parameter. In the described preferred embodiments, the energy wave is a sonic wave, such that the body of soft elastomeric material serves as an acoustical channel between the transmitter and receiver.

RELATED PATENT APPLICATION

This application is a National Phase Application of PCT/1L2004/000138having International Filing Date of 12 Feb. 2004, which claims thebenefit of U.S. Provisional Patent Application No. 60/447,017 filed 13Feb. 2003 and the benefit of U.S. Provisional Application No.60/483,110,filed 30 Jun. 2003. The contents of the above Application are allincorporated herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present application is related to: International ApplicationPCT/IL00/00241 published Nov. 9, 2000 as International Publication No.WO 00/67013; International Application PCT/IL02/00854 filed Oct. 24,2002, Published May 1, 2003 as International Publication No. WO03/036321; International Application PCT/IL02/00983, filed Dec. 5, 2002,published Jun. 12, 2003 as International Publication No. WO 03/048668;and U.S. Pat. No. 6,621,278 issued Sep. 16, 2003, the contents of whichapplications and patent are incorporated herein by reference in theirentirety.

The above-cited applications and patent relate to methods and apparatusfor measuring, with extremely high sensitivity, various parametershaving a known or determinable relationship with respect to the transittime of an energy wave (electromagnet or sonic) through a medium (solid,liquid or gas). Briefly, this is done by transmitting through the mediuma cyclically-repeating energy wave; receiving the energy wavetransmitted through the medium; detecting a predetermined fiducial pointin the received energy wave; continuously changing the frequency of thetransmission of the energy wave in accordance with the detected fiducialpoint of each received energy wave such that the number of wavesreceived is a whole integer; and measuring the changes in frequency toproduce a measurement of changes in transit time of the energy wave fromthe transmitter to the receiver, and thereby a measurement of thepredetermined parameter.

The above-cited applications and patent described many implementationsof such a method and apparatus in many fields, both medical andnon-medical, for providing measurements having an extremely high degreeof sensitivity. The described implementations included those whichproduced changes in the transit distance, and/or energy velocity inaccordance with changes in the predetermined parameter measured. Varioustypes of sensors were also described for measuring changes in thetransit distance, including deformable membranes, bellows,spring-mounted members, and displaceable plungers.

OBJECTS AND BRIEF SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide such apparatus with anew type of sensor making the apparatus particularly sensitive formeasuring displacements with extremely high sensitivity thereby enablingthe apparatus to accurately detect virtually any condition, or measurevirtually any parameter, inducing, induced by, or otherwise accompanyinga displacement. Examples of conditions so detected are very quick orsmall motions accompanying respiration and heart activity; and examplesof parameters so measured, as described below, include pressure,torsion, linear acceleration, weight, temperature, angular velocity,linear velocity, liquid density, depth in a body of liquid, magneticfield strength, respiration rate, blood pulse rate and blood pressure.

Another object of the present invention is to provide a novel sensorparticularly useful in such apparatus.

According to one aspect of the present invention, there is providedapparatus for measuring a predetermined parameter having a known ordeterminable relationship with respect to the transit time of an energywave through a medium, comprising: a sensor for sensing thepredetermined parameter, the sensor including a transmitter fortransmitting energy waves through the medium and a receiver forreceiving the energy waves transmitted by the transmitter; and a dataprocessor for measuring the transit time, or changes in the transittime, of energy waves from the transmitter to the receiver to therebyproduce a measurement of the predetermined parameter; characterized inthat the sensor includes a body of soft elastomeric material having hightransmissivity and low attenuation properties with respect to the energywaves, the transmitter and receiver being embedded in spaced relation toeach other, in said body of soft elastomeric material such that theparameter, when sensed by the sensor, produces a displacement of thetransmitter relative to the receiver, whereby measuring the transittime, or changes in the transit time, of the energy waves from thetransmitter to the receiver provides a measurement of the displacementof the transmitter relative to the receiver, and thereby of thepredetermined parameter.

The invention is particularly useful, and is therefore described below,with respect to applications in which the energy waves are sonic waves,whereby the transmission channel between the transmitter and receiver isan acoustical channel. It will be appreciated, however, that theinvention could also be implemented in applications where the energywaves are electromagnetic waves, e.g., light, infra-red or RF,particularly when the modulating technique described for example in U.S.Pat. No. 6,621,278 is used.

According to another aspect of the present invention, there is provideda sensor for sensing a predetermined parameter having a known ordeterminable relationship with respect to the transit time of an energywave through a medium, comprising: a body of soft elastomeric materialhaving high transmissivity and low attenuation properties with respectto the energy waves; and a transmitter and receiver embedded within thebody in spaced relation to each other such that the energy wavesreceived by the receiver are those transmitted by the transmitter afterhaving traversed at least a portion of the body of soft elastomericmaterial.

As will be described more particularly below, particularly good resultsare obtainable when sonic waves are used and the elastomeric material isa silicone elastomer having a Shore A hardness of 5-40, preferably 7-20.A Shore A hardness of about 10 was found most preferred in theapplications described below.

Other aspects, advantages and applications of the invention aredescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a block diagram broadly illustrating measuring apparatusincluding one form of sensor in accordance with the present invention;

FIG. 2 is a block diagram more particularly illustrating the control andprocessing circuitry (CPC) in the apparatus of FIG. 1;

FIG. 3 illustrates another sensor construction in accordance with thepresent invention;

FIG. 4 illustrates an acceleration-type sensor construction inaccordance with the present invention;

FIGS. 5-8 illustrate further constructions of sensors in accordance withthe present invention and several applications of such sensors;

FIGS. 9 a-9 c illustrate further applications of the present inventionfor detecting cessation of breathing (apnea detector), or for detectingmovements, respiration, pulse rate, or other conditions of anindividual;

FIG. 10 illustrates an application of the invention for use to preventbedsores;

FIG. 11 illustrates an anti-snoring application of the invention;

FIGS. 12-14 illustrate various constructions of sensors in accordancewith the present invention for monitoring pulse rate;

FIG. 15 illustrates an application of the invention for non-invasivelymeasuring blood pressure according to the oscillometric method;

FIG. 16 illustrates an application of the invention for measuring torquein a transmission system, e.g., in a vehicle;

FIG. 17 illustrates an application of the invention for monitoring avehicle seat, e.g., in order to detect the presence, weight, respirationactivity, cardiac activity, etc., of an occupant, e.g., to control anair bag;

FIGS. 18 a-18 c illustrate the invention embodied in a matrix of sensorsfor use as a keyboard or as a pressure distribution sensor;

FIGS. 19 and 20 illustrate the invention embodied in a pressure gaugefor indicating the pressure in a pressurized container and pipe line,respectively;

FIG. 21 illustrates in the invention embodied in a scale for weighingobjects;

FIG. 22 illustrates the invention embodied in an immersible sensor formeasuring the density of the liquid in which it is immersed, or thedepth at which the sensor is immersed;

FIG. 23 illustrates the invention embodied in a magnetic field sensorfor measuring the strength of a magnetic field;

FIG. 24 illustrates the invention embodied in an instrument formeasuring angular velocity and/or tangential acceleration of a rotatingbody;

FIG. 25 illustrates the invention embodied in a Pitot tube for measuringthe velocity of an object through a fluid medium;

FIG. 26 illustrates the invention embodied in an acceleration-typesensor;

FIG. 27 illustrates a further construction of a sensor in accordancewith the invention;

FIG. 28 illustrates the sensor of FIG. 27 implemented as anacceleration-type sensor;

FIG. 29 is a three-dimensional view; and FIG. 30 is an exploded view,illustrating the sensor of FIG. 27 implemented as a pressure sensor;

FIG. 31 illustrates the sensor of FIG. 27 embodied in an elastic belt orband sensor of extremely high sensitivity to be applied to a person fordetecting respiratory or cardiac activity;

FIG. 32 illustrates the invention embodied in a sensor applied to alarge surface, such as an airfoil, for detecting pressure distributionand/or deformation thereof;

FIG. 33 illustrates the invention embodied in a cellular telephonehandset or other hand-held portable electrical device;

FIG. 34 is a fragmentary sectional view of a portion of FIG. 33illustrating the sensor thereof;

FIG. 35 is a top view of the sensor of FIG. 34;

FIG. 36 is a view corresponding to that of FIG. 34 but illustrating thesensor as being of the acceleration-type to sense various types ofmotions, such as walking or running, as well as motions of respiratoryand cardiac activity;

FIG. 37 illustrates the hand-held portable electrical device of FIG. 33used as a pedometer;

FIG. 38 is a sectional view illustrating a differential-type pressuresensor constructed in accordance with the present invention;

FIG. 39 is a plan view illustrating a temperature-compensated forcesensor constructed in accordance with the present invention;

FIG. 40 a illustrates another sensor constructed in accordance with thepresent invention particularly useful for measuring weight or certainother forces;

FIG. 40 b is a three-dimensional view illustrating the securing devicein the sensor of FIG. 40 a;

FIG. 41 is a three dimensional view illustrating another sensorconstructed in accordance with the present invention particularly usefulfor measuring or detecting extremely small forces, such as thoseresulting from respiratory activity or cardiac activity;

FIG. 42 is a sectional view illustrating yet another sensor constructedin accordance with the present invention.

FIG. 43 illustrates an apnea monitor apparatus including the sensor ofFIG. 42 for sensing both respiratory and cardiac activity andcontrolling a vibrator and/or alarm in response thereto;

FIG. 44 is a block diagram illustrating an improvedfrequency-measurement system particularly useful in apparatusconstructed in accordance with the present invention;

FIG. 45 is a block diagram more particularly illustrating thefrequency-measurement system of FIG. 44;

FIG. 46 is a diagram illustrating an implementation of the invention toprovide for temperature-compensation;

FIG. 47 is a block diagram illustrating a system constructed inaccordance with FIG. 46 to provide temperature compensation;

FIG. 48 illustrates an improved system constructed in accordance withFIG. 46 to provide temperature-compensation;

FIG. 49 is a diagram helpful in explaining one manner of implementingthe invention as a highly stabilized frequency generator; and

FIG. 50 is a block diagram illustrating a frequency-generator circuitconstructed in accordance with the diagram of FIG. 49.

It is to be understood that the foregoing drawings, and the descriptionbelow, are provided primarily for purposes of facilitating understandingthe conceptual aspects of the invention and various possible embodimentsthereof, including what is presently considered to be a preferredembodiment. In the interest of clarity and brevity, no attempt is madeto provide more details than necessary to enable one skilled in the art,using routine skill and design, to understand and practice the describedinvention. It is to be further understood that the embodiments describedare for purposes of example only, and that the invention is capable ofbeing embodied in other forms and applications than described herein.

DESCRIPTION OF PREFERRED EMBODIMENTS

As indicated earlier, the present invention relates to apparatus formeasuring a parameter directly related to the displacement of one memberwith respect to another member, and particularly to a novel sensor foruse in such apparatus. The parameter to be measured may be pressure,torque, tension, linear acceleration, angular velocity, temperature,weight, liquid density, liquid depth, magnetic field strength,respiration, blood pulse, or virtually any other parameter inducing,induced by, or otherwise accompanying a change in the transit time of anenergy wave through a solid, liquid or gas medium.

The invention particularly provides a novel sensor which is capable ofmeasuring the respective parameter by detecting a displacement with anextremely high degree of sensitivity. The novel sensor provides anenergy-transmission channel which includes a body of soft elastomericmaterial, preferably a silicone elastomer, having highenergy-transmissivity and low energy attenuation properties, atransmitter, and a receiver in spaced relationship to each other suchthat precisely measuring the change in the transit time of energy wavesthrough the transmission channel from the transmitter to the receiverproduces a precise measurement of the respective parameter.

In the preferred embodiments of the invention described below, theenergy wave is a sonic wave, such that the transmission channel is anacoustical channel. It will be appreciated, however, that the energywave could also be an electromagnetic wave, such as light, infra-red,RF, etc., particularly when the modulating technique described in theabove-cited U.S. Pat. No. 6,621,278 is used.

Some embodiments described below are displacement-type sensors, whereina displacement is sensed and measured; whereas other describedembodiments are acceleration-type sensors, wherein the rate of change ofa displacement is detected and measured.

FIG. 1 is block diagram broadly illustrating one form of apparatusconstructed in accordance with the invention. The illustrated apparatusincludes a sensor 10 having one face exposed to the parameter, in thiscase pressure, to be measured, as shown by arrow P. Sensor 10 includes asonic transmitter 11 and a sonic receiver 12 embedded in spacedrelationship within a body of soft, pressure-compressible elastomericmaterial, generally designated 13. The opposite face of sensor 10, i.e.,opposite to that receiving the pressure P, is engaged by, or mounted on,a relatively rigid supporting member or base 14 such that theapplication of the pressure P will displace transmitter 11 towardsreceiver 12 in accordance with the magnitude of the applied pressure.Sensor 10 is thus a displacement-type sensor in that measuring thedisplacement or relative position of transmitter 11 with respect toreceiver 12 will produce a precise measurement of the pressure P.

The position of transmitter 11 with respect to receiver 12 is preciselymeasured in accordance with the method and apparatus described in theabove-cited International Applications and U.S. patent. Thus, theapparatus includes control and processor circuitry, generally designatedCPC, for controlling the transmitter 11 and receiver 12 such as toproduce a precise measurement of the change in relative positionsbetween the two. The control and processor circuitry CPC shown in FIG.1, and more particularly described below with respect to FIG. 2,includes a transmitter circuit 15, a receiver circuit 16, and adisplacement measurement circuit 17 measuring the change in spacingbetween transmitter 11 and receiver 12, and producing an output, e.g.,to a display 17 a, an alarm 17 b, and/or a control 17 c.

FIG. 2 more particularly illustrates the control and processor circuitryCPC of FIG. 1. As more particularly described in the above-citedInternational Patent Applications and U.S. Patent such circuitry isconstructed and operates as follows:

Initially, oscillator 21 is energized while switch 22 is closed so as tocause transmitter 11 to transmit a succession of sonic pulses until suchpulses are received by receiver 12. Once the pulses are received byreceiver 12, switch 22 is opened so that the pulses received by receiver12 are thereafter used for controlling the transmitter 11.

As shown in FIG. 2, the sonic signals received by receiver 11 are fed toa comparator 23 via its input 23 a. Comparator 23 includes a secondinput 23 b connected to a predetermined bias so as to detect apredetermined fiducial or reference point in the received signal. In theexample illustrated in FIG. 2, this predetermined fiducial point is the“zero” cross-over point of the received signal; therefore, input 23 b ofcomparator 23 is at a zero bias.

The output of comparator 23 is fed to an amplifier 24, e.g., amonostable oscillator, which is triggered to produce an output signal ateach fiducial point (zero cross-over point) in the signals received byreceiver 12. The outputs from amplifier 24 are fed via an OR-gate 25 totrigger the transmitter 11 for the next sonic pulse. Since switch 22 isopen, transmitter 11 will thus be triggered by each signal received bythe receiver 12 to transmit the next sonic pulse in the succession ofpulses.

It will thus be seen that the frequency of the output pulses or signalsfrom transmitter 12 will change with a change in the spacing between thetransmitter 11 and receiver 12. It will also be seen that the number ofwavelengths or pulses in the signal transmitted by transmitter 11 andreceived by receiver 12 will be a whole integer. This change infrequency by the transmitter 11, while maintaining the number of wavesbetween the transmitter and receiver 12 as a whole integer, enables aprecise determination to be made of the distance between the transmitterand receiver. The summing circuitry, including counter 26, counter 27,clock 28 and microprocessor 29, enables the detected frequencydifference, and thereby the measurement precision, to be increased by afactor “N”, such that the precision of the measurement can be preset,almost without limitation, by the selection of the appropriatefrequency, clock rate for clock 28, and summation factor “N” for counter27.

As further shown in FIG. 2, the output from microprocessor 29 of thecontrol and processor circuit CPC may be used for display, alarm and/orcontrol purposes, as schematically shown at 17 a, 17 b and 17 c.

Further details of the construction and operation of such an apparatusare available from the above-cited International Applications and U.S.Pat. No. 6,621,278, incorporated herein by reference. For example, U.S.Pat. No. 6,621,278 includes a modulation feature, and also a delay linefeature, which significantly extend the possible applications of suchapparatus for measuring various types of parameters.

Specific implementations of the method and apparatus described in theabove-cited International Applications and U.S. Patent, utilized sensorsin the form of deformable membranes, bellows, spring-mounted members, ordisplaceable plungers. However, it has now been found that utilizing asensor of the above-described construction illustrated at 10 in FIGS. 1and 2, namely one including a body of soft elastomeric material 13,preferably embedding the transmitter 11 and receiver 12 in spacedrelation to each other, enables considerably higher sensitivity to beattained of the displacement being detected and measured.

It will thus be seen that the body of soft elastomeric material 13between the transmitter 11 and receiver 12 defines an acoustical channelbetween the transmitter and receiver. It will also be seen that thepressure P applied to the sensor changes the effective length of thisacoustical channel such that, measuring the instantaneous length of thechannel by measuring the transit time of a sonic pulse from thetransmitter to the receiver, produces a measurement of the pressureapplied to the sensor. The sensor of FIGS. 1 and 2, therefore, is adisplaceable-type pressure sensor in which a measurement of thedisplacement, or change in effective length, of the acoustical channelproduces a measurement of the pressure applied to the sensor. Thecircuit illustrated in FIG. 2 detects displacement with particularlyhigh sensitivity, enabling a measurement of particularly high accuracyto be made of the force P applied to the sensor.

It will be appreciated that the displacement-type sensor illustrated inFIGS. 1 and 2 can also be used for producing highly accuratemeasurements of other parameters which change the effective length ofthe acoustical channel defined by the soft elastomeric material 13between the transmitter 11 and receiver 12. Examples of other parametersinclude torque, centrifugal force, respiratory pulsations, bloodpressure pulsations, weight, etc., as will be described moreparticularly below.

As will also be described more particularly below, the sensor couldinclude a weight acting as an inertia member to produce anacceleration-type sensor in which changes in the displacement aredetected and used for producing a measurement of the respectiveparameter. Such acceleration-type sensors are particularly useful wherethe displacements occur frequently or rapidly.

Preferred materials for the elastomeric body 13 in FIGS. 1 and 2 aresilicone rubber compounds, e.g., those supplied by Smooth-on Ltd. underthe Trademark “Dragon Skin” and “Dragon Skin Q”; those supplied byRhodia, Inc. of Cranbury, N.J. under the Trademark “Rhodorsil” RTV-585;and RTV Silicone rubber compounds supplied by General Electric Company.Preferably, the elastomeric material should have a Shore A hardness of5-60, and more preferably from 7-20. For many of the applicationsdescribed below, a Shore A hardness of 10 was found to produce bestresults.

Such materials have high sonic-wave transmissivity properties and lowsonic-wave attenuation properties. They are also characterized by aYoung's modulus of elasticity 10⁵ times lower than steel, and aPoisson's ratio of almost 0.5. These properties have been found toproduce the exceptional and unexpected sensitivity to detectingdisplacements attainable by sensors constructed according to the presentinvention.

The frequency of oscillator 21 would depend, to a large extent, on theparticular application of the sensor. In most of the applicationsdescribed below, the frequency of oscillator 21 would preferably be inthe range of 500-2000 kHz, preferably about 700 kHz.

FIGS. 3-39 illustrate examples of a number of constructions andapplications of displacement-type and acceleration-type sensors for usein the apparatus of FIGS. 1 and 2.

Thus, FIG. 3 illustrates a displacement-type sensor, therein generallydesignated 30, which also includes a sonic transmitter 31 and a sonicreceiver 32 embedded in an elastomeric body 33 mounted on a mountingmember 34 at the opposite face of body 33 to receive the pressure Pbeing measured. In this case, the elastomeric body 33 is formed with afirst leg 33 a in which the transmitter 31 is embedded, and a second leg33 b in which the receiver is embedded, such that the receiver receivesthe sonic pulses from the transmitter 31 via a bridge 33 c bridging thetwo legs. Such an arrangement thus provides an acoustical channel ofcompact construction having a relatively long sonic-wave transmissionpath between the transmitter and receiver.

FIG. 4 illustrates an acceleration-type sensor, therein generallydesignated 40, of a similar construction as in FIG. 3, to include atransmitter 41 embedded in one leg of an elastomeric body 43, a receiver42 embedded in another leg and communicating with the transmitter via abridge, and a mounting member 44 for mounting the elastomeric body 43.In this case, however, the bridge end of the elastomeric body 43 carriesa weight 45, which acts as an inertia member, to produce the force to beapplied to the elastomeric body upon its displacement. Sensor 40 maythus be used as an accelerometer for measuring linear acceleration of abody. As will be described below, such a sensor may also be used tomeasure changes in the angular or rotational velocity of a body bysensing changes in the centrifugal force generated by the weight duringthe rotation of the body.

FIG. 5 illustrates an example of an application of a sensor, thereingenerally designated 50, for application to the chest of a person inorder to measure or detect the respiration or cardiac rate of theperson. For such application, the elastomeric body, therein designated53, containing the transmitter 51 and receiver 52 embedded therein atspaced locations, would be secured, e.g., by an elastic band 55, to thechest of the patient, while applying a predetermined pressure thereto,such that the changes in the locations between the transmitter andreceiver, produced by the pulsatile movements of the chest, will providea measurement of the respiration rate and/or cardiac rate of theindividual.

Sensor 50 illustrated in FIG. 5 may be of the accelerometer type asillustrated in FIG. 4, or the displacement-type of FIG. 3, as well as ofother constructions described below.

FIG. 6 illustrates a sensor, therein generally designated 60, which maybe of the same construction as in FIG. 5, except that it is to beapplied to the wrist of the individual, and therefore includes awrist-band 65, for purposes of detecting and measuring the individual'spulse. Sensor 60 illustrated in FIG. 6 may also be of the accelerometertype or of the displacement-type as described above with respect to FIG.5.

FIG. 7 illustrates a sensor 70 of similar construction as in FIGS. 1 and2, to include a transmitter 71 and receiver 72 embedded in spacedrelationship within the elastomeric body 73. In this case, one side ofbody 73 carries a printed circuit board 74 which includes at least partof the control and processor circuitry CPC of FIGS. 1 and 2. The otherside of elastomeric body 73 may carry another printed circuit board 75including the remainder circuitry and/or a weight to enable the sensorto serve as an accelerometer, as in FIG. 4.

FIG. 8 illustrates a sensor 80 constructed in accordance with thepresent invention to serve as a finger probe for sensing pulsatile bloodflow in a person's finger and the temperature of the finger. For thispurpose, sensor 80 includes an elastomeric body 83 having a transmitter81 and receiver 82 embedded therein in spaced relation, as describedabove, to produce an output for measuring displacement, as shown at 84.

In this case, however, elastomeric body 83 includes a second sonictransmitter 85 and second sonic receiver 86 spaced therefrom but bridgedby a path 87 of a temperature-sensitive material (e.g., metal) exposedto the temperature of the finger. Since the velocity of the sonic wavesbetween transmitter 85 and receiver 86 is changed by a change intemperature of the metal path 87, the control and processor circuitryCPC (FIGS. 1, 2) will produce an output of the measured temperature, asshown at 88, as described more particularly in the above-citedInternational Applications. This temperature measurement can beoutputted to a display for viewing, and/or can be used for providingtemperature compensation of the displacement measurement 84, asschematically shown by block 89 in FIG. 8.

It will thus be seen that the device illustrated in FIG. 8 actuallyincludes two sensors each having its own acoustical channel for sensinga predetermined parameter. Thus, the soft elastomeric material 83between transmitter 81 and receiver 82 defines one acoustical channelwhich senses displacement; whereas the temperature-sensitive path 87between transmitter 85 and receiver 86 defines a second acousticalchannel which senses temperature. Both channels produce a change in thetransit time of a sonic wave from the transmitter to the receiver of therespective channel in accordance with the parameter being sensed. Thus,the acoustical channel between transmitter 81 and receiver 82 defined bythe soft elastomeric material 83 between them changes its effectivelength in response to the parameter (pressure) to be measured, whereasthe acoustical channel between transmitter 85 and receiver 86 changesits sonic-wave transmissivity in response to the measured parameter(temperature).

FIGS. 9 a-9 c illustrate the apparatus of the present invention used formonitoring a condition of an individual in a bed. It has been found thatthe extremely high sensitivity of the measuring apparatus enablesdetection, not only of movements, breathing or cessation of breathing(apnea), but also heart activity of the individual.

Thus, as shown in FIG. 9 a, a sensor (90 a-90 c) is inserted under eachof the four legs of the bed BD. As shown in FIG. 9 b, each sensor is ofa construction as described above, to include a transmitter 91 and areceiver 92 embedded in spaced relationship to each other in a body 93of elastomeric material mounted on a flat mounting member 94. Where aleg of the bed is mounted on a wheel or roller, as shown at 95, theupper end of the sensor 90 is provided with a cap 96 shaped toaccommodate the roller or wheel 95. FIG. 9 c schematically illustratesthe electrical circuitry connecting the four sensors 90 a-90 d in seriesto produce an output to the control and processor circuit 98.

It will thus be seen that the arrangement illustrated in FIGS. 9 a-9 cenables detecting the vital signs (respiration, cardiac activity), aswell as movements, of the occupant of the bed. Instead of connecting theoutputs of the sensors in series for integration as in FIG. 9 c, theoutputs could also be connected in parallel, where each output signal isindependent from the others. A preferred alternative would be to havethe feedback from the receiver to the transmitter to pass along the fullloop of several sensors so that the resulting frequency depends on thetotal delay in all the sensors, that is, the receiver of one sensorwould trigger the transmitter of the next sensor in the loop, such thatthe system requires only one measurement channel. Also, only one or twosensors could be used. The wires used to connect the sensors can beattached to the bed frame. The sensors can be made waterproof and can bedesigned of such high sensitivity so as to be capable of sensing verysmall movements or vibrations involving forces of a few grams.

FIG. 10 illustrates the sensor of the invention applied to preventbedsores. For this purpose, a plurality of sensors 100 a, 100 b-100 n,may be located, in any desired number and pattern, under a mattress 101to sense a particular area of the individual's body in contact with themattress for any movement, changes in blood flow, etc. All the sensorsare connected to a control and processor circuitry 102 effective, if nomovement is detected, or if the blood flow rate drops in a predeterminedarea within a predetermined time period, to actuate a bed shifter 103 inorder to shift the mattress or the bed such as to cause a change in theposition of the individual, and thereby to reduce or eliminate thechances of producing bedsores.

It has been found that sensors constructed in accordance with thepresent invention enable such a high degree of sensitivity to beobtained that they can be located under the mattress 101, within themattress, or on the upper surface of the mattress so as to be in directcontact with the individual's body.

While FIG. 10 illustrates the system as applied to a mattress foravoiding bedsores, the same system can be included in the seat pad of awheelchair. Also, while the device controlled is a shifting device for abed, mattress, or pad shifter, a massaging or pulsating device could becontrolled to massage or pulsate the affected area. In addition, theycan serve as apnea monitors; and where the bed is a double bed to beoccupied by two persons, two such sensors may be used, one on each side,connected to a common alarm to be actuated if a monitored emergencycondition (i.e., a respiration or cardiac condition) is detected withrespect to either bed occupant.

FIG. 11 illustrates an application of the invention as an anti-snoringdevice. When so used, one or more of the sensors, shown at 110 a-110 n,preferably of the acceleration-type, may be applied to the chest, bed,stand, and/or pillow of the individual to produce outputs to the controland processor circuitry 112. The latter circuit would be programmed torecognize outputs indicating a “snoring” occurrence and automatically toactuate a pillow shifter 113 to shift the pillow, or to produce anotherdisturbance (e.g., a gentle “poke”) to the individual in an attempt tointerrupt the snoring. The arrangement illustrated in FIG. 11 thusprovides a biofeedback system in which the user is disturbed each timesnoring is detected, with the object of slowly decreasing to zero theamount of snoring.

FIGS. 12-14 illustrate the invention applied to various types of fingerprobes for measuring pulse rate, blood pressure, or other cardiovascularcondition of the individual.

In FIG. 12, the sensor, therein designated 120, is of ring shape to bereceived on a finger of the individual. It includes a transmitter 121and a receiver 122 embedded within a body of elastomeric material 123 ofannular configuration. The body 123 is formed on one side with an aircavity 124, to thereby define an acoustical channel on the other sidefor the sonic pulses from the transmitter 121 to the receiver 122. Asschematically shown in FIG. 12, transmitter 121 and receiver 122 areconnected to a control and processor circuit 125 which produces ameasurement of the changes in the length of the sonic path resultingfrom the pulsatile blood flow through the finger.

FIG. 13 illustrates a similar sensor 130 as in FIG. 12, except that thetransmitter 131 and receiver 132 are located in radial alignment on oneside of the elastomeric body 133 to produce a radially-extendingacoustical channel, and the elastomeric body is of elliptical shape soas to apply a compressive, but non-occluding, force to the fingerreceived within the opening of the sensor. As described above, thepulsatile blood flow through the individual's finger will be sensed bythe change in relative position between the transmitter 131 and receiver132, to produce a measurement of the pulse rate.

FIG. 14 illustrates a finger-probe type sensor 140, similar to that ofFIGS. 12 and 13, including a transmitter 141 and receiver 142 embeddedat spaced locations within an elastomeric body 143 of ring-shape. Inthis case, however, the ring is closed by a band 144, which applies apredetermined compressive force to the finger received within the ring.The presence of band 144 also causes the sonic pulses to be directedthrough the desired acoustical path from the transmitter 141 to thereceiver 142.

FIG. 15 illustrates a sensor, therein designated 150, used in a systemfor measuring blood-pressure according to the oscillometric method. Thesystem illustrated in FIG. 15 includes a cuff 151 inflatable via a tube152 by a manual pump 153 and a one-way valve 154. Tube 152 furtherincludes a valve 155 which automatically closes when the cuff has beeninflated to the desired pressure. When so inflated, the pressure withinthe cuff 151 is gradually decreased by a small hole 156 formed in thecuff.

The pressure within the cuff is continuously monitored by sensor 150connected to the cuff by means of a tube 157. Sensor 150 is electricallyconnected to the control and processing circuit 158 to control thesensor in the manner described above, and also to output the cuffpressure measurements as sensed by the sensor.

Cuff 151 is preferably dimensioned so as to be received on a finger ofthe subject, and thus to sense the arterial blood flow through thefinger. It will be appreciated, however, that cuff 151 could also bedimensioned to enclose an arm of the person, as in the conventionaloscillometric method of measuring blood pressure.

According to this method of blood pressure measurement, cuff 151 isinflated by pump 153 to a pressure above the patient's systolicpressure, whereupon valve 155 automatically closes. The small hole 156in cuff 151 (or in connecting tube 157) gradually reduces the pressurewithin the cuff. Pressure sensor 150, controlled by the control andprocessing circuitry 158, continuously measures the pressure within thecuff and produces outputs of such measurements.

According to this technique of blood pressure measurement, the pressurefluctuations within the patient's artery resulting from the beats of thepatient's pulse are transferred to the inflated cuff 151, causing slightpressure variations within the cuff as the cuff is gradually deflated.Thus, the output from the pressure sensor 150, as appearing in itscontrol and processing circuitry 158, would generally be a DC componentrepresenting the decreasing cuff pressure, and a serious of smallperiodic variations associated with the beats of the patient's pulse.These small variations are often referred to as “oscillation complexes”,or simply “oscillations”. A patient's blood pressure may be estimated inaccordance with the known oscillometric method of blood pressuremeasurement based on an analysis of these oscillation complexes.

Because of the exceptionally high sensitivity to displacementsattainable by sensor 150 constructed in accordance with the presentinvention, such a sensor is particularly useful for this method of bloodpressure measurement.

FIG. 16 illustrates the application of the invention for measuringtorque, e.g., in a drive shaft of a motor vehicle transmission system.It also illustrates another feature of the present invention, namely foreliminating or reducing the effects of temperature drifts (or othertransient effects) in the measurements.

The apparatus illustrated in FIG. 16 includes two sensors 160 a, 160 b,each of the same construction as described above to include atransmitter 161 and a receiver 162 embedded within a body of elastomericmaterial 163 defining an acoustical channel. The two sensors 160 a, 160b are fixed at one of their ends to the flywheel 165 of the vehicletransmission system, with the opposite ends facing and aligned with eachother.

The drive shaft 166 of the vehicle drive system is provided with an arm167 which is located between, and secured to, the facing ends of the twosensors 160 a, 160 b. The two sensors are connected to the control andprocessor circuitry 165 in a subtractive manner, such that the outputfrequency of one sensor will be subtracted from that of the othersensor.

Assuming the drive shaft 166 is rotating in the direction of the arrow(clockwise), it will be seen that an increase in the torque applied tothe drive shaft will compress sensor 160 a, and will expand sensor 160b. Thus, the output frequency of sensor 160 a will be increased (+Δf)while the output of sensor 160 b will be decreased (−Δf). On the otherhand, the temperature drift (Δf_(T)), velocity, or other transientinfluences, will be the same with respect to both sensors. Accordingly,by subtracting the output of sensor 160 b from that of sensor 160 a,there is produced an output torque (T) which is a function of 2Δf, sincethe temperature drift component of each frequency is cancelled from theother. Thus:T=f ₁ −f ₂=(f ₀ +Δf+Δf _(T))−(f ₀ −Δf+Δf _(T))=2Δf

The arrangement illustrated in FIG. 16 thus, not only eliminates orreduces the effects of temperature drift (as well as other transientinfluences), but also significantly increases the output signal. Inaddition, since the forces applied to the two sensors along any axis,other than the axis AS as illustrated in FIG. 16, will have a similarinfluence on the output frequencies of the two sensors as thetemperature drift influence, those forces (such as centrifugal forcesdue to velocity variations) will also tend to cancel out when the outputfrequency of one sensor is subtracted from the other, such that axis ASin FIG. 16 will be substantially the only axis of sensitivity.

It will be appreciated that the foregoing features in the applicationillustrated in FIG. 16, which enhance the accuracy of the measurements,may also be used in the many other applications, such as thosepreviously described or to be described below.

FIG. 17 illustrates a further application of the invention applied to avehicle seat, e.g., for monitoring the condition of the occupant of theseat, and/or for controlling an airbag in accordance with the presenceor absence of an occupant, or the weight of the occupant (e.g., todistinguish a child from an adult). Thus, FIG. 17 illustrates a vehicleseat VS including one or more of the sensors 170 a-170 n carried atvarious locations thereon, according to the particular application. FIG.17 further illustrates the control and processor circuitry 176 forcontrolling the various sensors and for producing the desired outputs,e.g., as described above with respect to FIGS. 1 and 2, but furtherincluding an air bag actuator 177, if the outputs are intended tocontrol the actuation of the air bag. For example, the air bag could becontrolled so as to be actuated only when breathing or a blood pulse hasbeen detected from the respective vehicle seat to indicate the seat isoccupied. The detected respiration and/or blood pulse rate could also bedetected, together with the weight of the occupant, e.g., to distinguisha child from a small adult, and to control the air bag actuationaccordingly.

FIGS. 18 a-18 c illustrate a sensor assembly, generally designated 180,including a plurality of sensors 180 a-180 n arranged in a matrix, witheach sensor including a sonic transmitter 181 and a sonic receiver 182embedded in spaced relationship within an elastomeric body 183.Elastomeric body 183 may be common for all the sensors 180 a-180 n, ormay be a separate body for each such sensor. All the transmitters andreceivers are connected to a common control and processing circuit 185via a scanner 186 which sequentially scans the sensors in order tocontrol them and to receive their outputs.

Such a sensor assembly as illustrated in FIGS. 18 a-18 c may thus beused in several of the foregoing applications, e.g., to detect vitalsigns in the bed or wheelchair application of FIGS. 9 a-9 c, to preventbed sores in the application of FIG. 10, or to sense weight,respiration, and/or cardiac rate in an air bag control apparatus of FIG.17. Since the operating elements of the assembly are all embedded withina plastic (the elastomeric material), such a sensor assembly could alsobe used as a water-proof keyboard or other input device. The water-proofproperty of the sensor assembly also enables it to be used, insingle-sensor units or multiple-sensor units, as electrical switches orother input devices for controlling various types of appliances, such aswashing machines, water heaters, or the like, that may involve a dangerwhen exposed to water.

FIG. 19 illustrates a sensor 190 according to any of the aboveconstructions used for measuring the pressure within a pressurizedcontainer 195. FIG. 20 illustrates such a sensor 200 used for measuringthe pressure within a pressurized pipe 205.

FIG. 21 illustrates sensor assemblies 210 constructed as described abovefor supporting a scale 215 in order to measure the weight of an objectplaced on the scale. In the example illustrated in FIG. 21, the scale215 is supported in suspension at each of its four corners by anassembly of two sensors 210 a, 210 b, arranged in a differential orsubtractive relationship as described above with respect to FIG. 16 inorder to compensate for temperature.

FIG. 22 illustrates a sensor, therein designated 220, used for measuringthe density of a liquid 225 in which the sensor is immersed. Forexample, the liquid could be water within a swimming pool 226 whereinthe measured density would indicate the concentration of chlorine in, orthe pH of, the water. Preferably, sensor 220 illustrated in FIG. 22 alsoincludes a temperature-sensitive sensor element 227, as described abovewith respect to FIG. 8, e.g., for providing temperature compensation forthe measurement outputted by sensor 220. Sensor 220 can also be used asa depth gauge for measuring the depth in which it is immersed in a bodyof water or other liquid.

FIG. 23 illustrates a sensor constructed in accordance with the presentinvention for measuring the intensity of a magnetic field. Such asensor, generally designated 230, could be any of the above-describedconstructions, to include a sonic transmitter 231 and a sonic receiver232 embedded in spaced relationship to each other in a body ofelastomeric material 233 defining the acoustical channel of the sensor.In this case, however, one or both ends of the body of elastomericmaterial would carry a magnet, as shown at 234, such as to produce aforce compressing or expanding the acoustical channel in accordance withthe magnetic field sensed by the sensor.

FIG. 24 illustrates an assembly including two acceleration-type sensors240 a, 240 b mounted on a body 241 rotatable about a rotary axis 242.Both sensors 240 a, 240 b include a weight 245 a, 245 b, respectively,as described above with respect to FIG. 4. In this case, however, sensor240 a is carried by rotary body 241 such that its weight 245 a islocated radially outwardly; therefore sensor 240 a would provide ameasurement of the centrifugal force produced by the weight, and therebya measurement of the rotational velocity of body 241. On the other hand,sensor 240 b is oriented such that its weight 245 d extends tangentiallywith respect to that sensor, and therefore its output would be ameasurement of the linear velocity of rotary body 241.

FIG. 25 illustrates a sensor, generally designated 250, constructed inaccordance with the present invention for measuring the linear velocityof an object in a fluid medium, e.g., for measuring the speed of anaircraft through air, based on the Pitot tube measurement technique. ThePitot tube is oriented in the direction of travel. It includes a pair ofchambers 251, 252 at one end of the Pitot tube, a main passageway 253oriented in the direction of travel of the vehicle and communicatingwith chamber 251, and a plurality of openings 254 orientedperpendicularly to the direction of travel of the vehicle andcommunicating with both chambers 251, 252.

It will thus be seen that the pressure within chamber 251 is the totalpressure (P_(T)), being the sum of the dynamic pressure (P_(P)) sensedvia passageway 253, and the static pressure (P_(S)) sensed viapassageways 254; whereas the pressure within chamber 252 will be onlythe static pressure (P_(S)) sensed via passageways 254.

The total pressure within chamber 251 is measured by sensor 250 a, andthe static pressure within chamber 252 is measured by sensor 250 b. Bothsensors may be of any of the above-described constructions, to includean acoustical channel defined by a sonic transmitter and a sonicreceiver embedded in spaced relation within an elastomeric body.

It will be seen that the dynamic pressure (P_(D)) produced by thevelocity V can be determined by subtracting the static pressure (P_(S))sensed by sensor 250 b from the total pressure sensed (P_(T)) by sensor250 a. The so-determined dynamic pressure (P_(D)) may then be used fordetermining the velocity of the body according to the following knownequation:

$V^{2} = \frac{2\left( {P_{T} - P_{S}} \right)}{r}$wherein P_(T) is the pressure measured by sensor 250 a; P_(S) is thepressure measured by sensor 250 b; and r is the local value of airdensity.

FIG. 26 illustrates the invention embodied in an acceleration-typesensor, generally designated 260, including a housing 261. Housing 261serves as a mounting member for mounting the sensor to a patient's bodyPB, e.g., by an elastic belt 262 to detect respiration and/or cardiacactivity, in the manner illustrated in FIG. 5. In this case, however,sensor 260 includes an arm 262 pivotally mounted at one end 262 a tohousing 261. One face of the opposite end 262 b of arm 262 is secured,as by an adhesive, to one end of a body 263 of soft elastomeric materialdefining an acoustical channel between a sonic transmitter 263 a andreceiver 263 b embedded therein in spaced relation to each other. Theopposite end of the soft elastomeric body 263 is secured, as by anadhesive, to the inner surface of housing 261. The lower face of end 262b of pivotal arm 262 carries a weight 264, e.g., secured thereto by anadhesive.

The construction illustrated in FIG. 26 provides an extremely sensitiveacceleration-type sensor which detects the respiratory and cardiacmovements of the patient's body PB and produces a highly accuratemeasurement of such movements.

It will be appreciated that the acceleration-type sensor illustrated inFIG. 26 may be mounted to another surface of the patient's body, e.g.,the wrist or arm, in order to detect and measure the displacementsproduced by cardiac activity, i.e., blood pulses, of the patient. Suchan acceleration-type sensor may also be used in many non-medicalapplications, such as in seismic detectors, security fences, etc. wherehighly-sensitive detection or measurement of fast-action orhigh-frequency movements is required.

FIG. 27 illustrates a sensor, generally designated 270, wherein the softelastomeric material 271 is in the form of a narrow strip such as todefine a narrow acoustical channel between the spaced sonic transmitter272 and receiver 273. The sensor illustrated in FIG. 27 further includesa damper or sound absorbing material effective to absorb sonic wavesexcept those in the narrow acoustical channel. FIG. 27 illustrates thedampers as being pre-formed bodies 274, 275, at each of the oppositeends of the acoustical channel. A suitable material for the dampers 274,275 is relatively soft rubber having high sonic-wave attenuationproperties. While FIG. 27 illustrates the dampers applied just to theopposite ends of the acoustical channel, it will be appreciated thatsuch damper material could be applied over additional surfaces of theacoustical channel, such as the underlying surface.

FIG. 28 illustrates an acceleration-type sensor device 280 having astrip-type sensor element 270 of the construction illustrated in FIG.27. Thus, sensor 280 includes a housing 281 mounting sensor element 270in suspension between two posts 282, 283. Housing 281 further includes aweight 284 having a depending projection 285 at one end engageable witha mid-portion of sensor element 270. The opposite end (not shown) ofweight 284 is pivotally mounted to the housing 281 such that themid-portion of sensor element 270 is deflected by the displacement,(more particularly by the rate-of-change in the displacement) of weight284. The acceleration-type sensor device 280 illustrated in FIG. 28 thusalso provides a highly-sensitive means for detecting and/or measuringmovements, and may therefore also be used in the applications describedabove with respect to FIG. 26.

FIGS. 29 and 30 are assembly and exploded views respectively, of apressure sensor device 290 utilizing the strip-type sensor element 270of FIG. 27 for sensing pressure in a chamber within a housing. Sensor290 includes a housing 291 defining a chamber 292 communicating with aport 293 for a fluid whose pressure is to be measured. For this purpose,chamber 292 is closed by a membrane 293 carrying sensor element 270 ofthe construction described above with respect to FIG. 27 such that themembrane and the sensor element are deformable in response to thepressure within the chamber. For example, membrane 293 may be of a softrubber having high sonic-attenuation properties so as also to act as adamper to absorb sonic waves except those in the narrow acousticalchannel of sensor element 270.

Sensor device 290 further includes a block 295 and a cover 296 forsecuring membrane 294 over the pressure chamber 292. Block 295 is formedwith a cavity 297 providing access to the transmitter and receiver ofsensor element 270, and includes an electrical connector 298 for makingthe appropriate electrical connections to the sensor.

FIG. 31 illustrates a sensor device 310 particularly useful fordetecting and/or measuring elongation displacements of the sensor, suchas described above with respect to FIG. 5. Thus, sensor 310 includes astrip-type sensor element 270 of the construction described above withrespect to FIG. 27, having a narrow acoustical channel 271 of softelastomeric material between a sonic transmitter 272 and sonic receiver273. In the construction illustrated in FIG. 31, sensor element 270 ismounted on an elastic member 311, such as a chest band, for detectingrespiration and/or cardiac activity. Thus, the respiration and cardiacactivity by the patient will produce extensions and contractions ofelastic member 311 and of the soft elastomeric material 271 in thenarrow acoustical channel of sensor element 270, thereby enabling thesensor to detect and/or measure such respirations or cardiac activitywith a high degree of sensitivity.

Elastic member 311 of sensor element 270 is preferably of a material,such as soft rubber, having high sonic-wave attenuation properties, soas to absorb sonic waves except those in the narrow acoustical channeldefined by the sensor element 270.

FIG. 32 illustrates a sensor assembly, therein generally designated 320,for application to a surface of an object, such as an airfoil 321, tomeasure deformations thereof and/or pressure distribution thereon. Thus,the sensor assembly 320 includes a body of soft elastomeric materialshown at 322, of a large surface area applied to, and conforming to, thesurface of the airfoil 321. The soft elastomeric material body 322includes a plurality of sonic transmitter and receiver pairs, such asshown at 323 and 324, located within the body such that each pairdefines, with the portion of the soft elastic material 322 between them,a separate acoustical channel for detecting and/or measuringdeformations and/or pressure distribution on the surface of the airfoil321 occupied by the respective acoustical channel.

As an alternative arrangement, the deformations and/or pressuredistribution on the surface of airfoil 320 may be detected and measuredby a plurality of individual strip-type sensor elements 270, each of theconstruction as described above with respect to FIG. 27, fixed to thesurface of the airfoil.

FIG. 33 illustrates a hand-held portable electrical device, generallydesignated 330, such as a cellular telephone handset, PDA, or the like,incorporating a sensor 340 constructed in accordance with the presentinvention portable electrical device 330 may be of any conventionalconstruction. For purposes of example, it is shown as including a casing331 formed with a display window 332 and carrying a plurality of keys333 for dialing a telephone number or inputting other information.Sensor 340 included in electrical device 330 is more particularlyillustrated in FIGS. 34 and 35.

Sensor 340 illustrated in FIGS. 34 and 35 is a displacement-type sensor.It includes a body of soft elastomeric material 341 configured as abutton and received within a slot 334 formed in the housing 331. A sonictransmitter 342 and a sonic receiver 343 are fixed to the opposite sidesof the soft elastomeric body 341 such that the portion of that bodybetween the transmitter and receiver define an acoustical channel forthe sonic waves transmitted by the transmitter to the receiver. The softelastomeric material body 341 is formed with an outer convex surface 344projecting outwardly of housing 331 so as to be engageable by a bodypart of the user, as will be described below. Body 341 includesdeformable spacing elements 345, such as small spherical projectionsintegrally formed on the outer surface of body 341, spacing the innerfaces of the body from the sides of the housing 331, to permit expansionand contraction of the portion of body 341 between the transmitter 342and receiver 343 when the outer face 344 of the sensor is engaged by theuser's body part. The bottom of body 341, and the two sides of the bodynot occupied by the transmitter 342 and receiver 343, are preferablylined with sound absorbing material, as shown at 346, 347 and 348,respectively.

Sensor 340 may thus be used to detect and/or measure blood pulse rate bythe user applying a finger to the outer surface 344 of the elastomericbody 341 such that the pulsations will produce changes in the effectivelength (compressions and expansions) of the acoustical channel betweenthe transmitter 342 and receiver 343, thereby providing a highlysensitive detection and/or measurement of the user's blood pulse. Thehand-held unit may also be used for detecting and/or measuringrespiration, by pressing the outer surface 344 of the elastomeric body341 against the user's chest, such that the respiration of the userproduces the compressions and expansions of the acoustical channelbetween the transmitter 342 and receiver 343.

FIG. 36 illustrates a sensor 360 of similar construction as sensor 340illustrated in FIGS. 34 and 35, except that it includes a weight 361,serving as an inertia member to thereby make the sensor of theacceleration-type, i.e., responsive to the rate of change of thedefected displacements.

An important advantage in incorporating a displacement-type sensor(FIGS. 34, 35) or acceleration-type sensor (FIG. 36) into a cellulartelephone handset is that the measurements of pulse rate, respirationrate, etc., may be transmitted, via the telephone, to remote locationsfor viewing, consultation, further processing, storage, or the like.

A further possible application of such a handset, particularly whenincluding an acceleration-type sensor as illustrated in FIG. 36, is foruse as a pedometer. Thus, the compression and expansion of theacoustical channel between the transmitter and receiver produced whilethe user is walking or running will identify the steps made by the user,and thereby provide a measurement of the number of steps traversedduring any particular time period. For example, the handset could becalibrated for the distance traversed by the respective user during awalking step, and/or during a running step. Thus, by accumulating thecount of running or walking steps traversed by the user, afterpre-storing the length of each step, the handset could be used toprovide a measurement of the total distance traversed by the user.

FIG. 37 illustrates another arrangement, therein generally designated370, to enable a hand-held portable electrical device, such as shown inFIGS. 33 and 34, also to be used as a pedometer for measuring traverseddistances. Such an arrangement mounts the weight to a belt clip or thelike holder used for carrying the device on the body of the person.

Thus, FIG. 37 illustrates a holder 371 attachable in any conventionalmanner to the user's belt for carrying the portable electrical device330, with the sensor button 340 projecting outwardly towards anothersection 372 of the holder. Section 372 in turn pivotally mounts a weight373 from its upper end, as shown at 374, such that each step of movementof the individual carrying the portable electrical device 330 will causethe weight 371 to pivot against sensor 340, to thereby enable thatsensor to identify each step.

FIG. 38 illustrates a differential-type pressure sensor 380 constructedin accordance with the present invention. It includes a housing 381having a deformable membrane 382 dividing the interior of the housinginto two fluid chambers C₁, C₂ each having a port 383, 384, to beconnected to a pressure source such that the membrane deforms inaccordance with the differential pressure in the two chambers. A narrowacoustical channel of the construction illustrated in FIG. 27 is mountedon each of the opposite sides of membrane 382 so as to detect thepressure within its respective chamber according to the deformation ofthe membrane. Thus, one narrow acoustical channel 270 a, including atransmitter 272 a, receiver 273 a, and the two absorber elements 274 a,275 a, is mounted on one side of membrane 382; and a second narrowacoustical channel 270 b, including its transmitter 272 b, receiver 273b, and absorber elements 274 b, 275 b, is mounted on the opposite sideof the membrane. Housing 381 further includes an electrical connector385, 386, for each of the narrow acoustical channels 270 a, 270 b. Thus,connector 385 for acoustical channel 270 a includes two terminals 385 a,385 b for its transmitter 272 a; two terminals 385 c, 385 d for itsreceiver 273 a; and a fifth terminal 385 e for a shielding electrodeprovided for the respective acoustical channel. Connector 386 includescorresponding terminals for the elements in its acoustical channel 270b.

It will be seen that the differential pressure in the two chambers C₁,C₂ on opposite sides of membrane 382 will produce a correspondingdeformation in the membrane, which deformation will be measured by thetwo acoustical channels 270 a, 270 b.

FIG. 39 is a plan view illustrating a force sensor 390 also constructedwith two narrow acoustical channels of the type described above withrespect to FIG. 27 to produce a temperature-compensated measurement offorce. The force sensor 390 illustrated in FIG. 39 includes a mountingmember 391 mounting a deformable member 392, such as a circular membrane(e.g., of rubber), which carries one narrow acoustical channel 270 c onone face, and another narrow acoustical channel 270 d on the oppositeface, the latter therefore being shown in broken lines. The force to bemeasured is applied between two force-receiving members 393, 394,aligned with each other along an axis A_(S), which defines theforce-sensitive axis. Thus, when a compressive force is applied alongaxis A_(S), the mounting member 391, as well as the circular membrane392 on which the two acoustical channels 270 c, 270 d are mounted, isdeformed as shown by broken lines in FIG. 39, such as to be contractedalong the force-sensitive axis A_(S), and to be expanded along the axisperpendicular to axis A_(S).

As shown in FIG. 39, one acoustical channel 270 d is mounted inalignment with axis A_(S), whereas the other acoustical channel 270 c ismounted along the axis perpendicular to axis A_(S). Accordingly,acoustical channel 270 c will increase in length according to the forceapplied, whereas acoustical channel 270 d will decrease in length. Theoutputs of the two acoustical channels are connected in a subtractivemanner as described above with respect to FIG. 16, such that theinfluence of the temperature cancels out, thereby making the sensorinsensitive to temperature variations.

FIG. 40 a illustrates a sensor assembly for use in measuring weight orother applied forces, whereas FIG. 40 b illustrates one of the securingdevices, generally designated 400, included in the sensor assembly ofFIG. 40 a. The weight or other force to be measured is applied to apanel 400, as shown by arrow F, of generally rectangular configurationand secured at each of its four corners by one of the securing devices400 (two of which are shown in FIG. 40 a). Each of the securing devices400 includes a pair of parallel arms 403, 404, joined at one end by aU-bend 405. One of the arms 404 is formed with a stepped extension 404 aat its open end to thereby increase the spacing between its open end 404a and the open end of the other arm 403. The U-bend end of arm 403 issecured by fastener 406 to plate 401 receiving the applied force, andthe U-bend end of the other arm 404 is secured by another fastener 407to the frame 402, such that the force F applied to panel 401 flexes theU-bend 405 of each of the securing devices 400.

A narrow-strip type sensor of the construction illustrated in FIG. 27,therein generally designated 270, is secured between arm 403 and theextension 404 a of arm 404 at the open end of each of these securingdevices 400. Each sensor 270 is of the construction described above withrespect to FIG. 27, to include an acoustical channel of elastomericmaterial between a sonic transmitter and a sonic receiver, such that thecontraction (or elongation) of the acoustical channel provides ameasurement of the force applied to the respective securing device 400.

FIG. 41 illustrates another narrow-strip type sensor, therein generallydesignated 410, constructed in accordance with the present invention. Inthis case, the narrow-strip sensor is fixed to the outer surface of abody 411 of pressure-deformable material of cylindrical configuration toextend around at least a part of the circumference of the body. Thus, asshown in FIG. 41, the body of pressure deformable material 411 is formedwith an annular recess 412 midway between its opposite faces andextending for at least a part of its circumference. Fixed within recess412 is a narrow-strip type sensor of the construction illustrated inFIG. 27, including a narrow strip 413 of an elastomeric material, atransmitter 414 at one end, and a receiver 415 at the opposite end.Preferably, the sensor further includes, at its opposite ends, damperelements 416, 417 of a sound absorbing material to suppress reflectedsonic waves and to confine the sonic waves generated by the transmitter414 to the narrow strip 413 of the elastomeric material.

It will thus be seen that when pressure is applied to the opposite facesof the cylindrical body 411, the body decreases in thickness andincreases in diameter, thereby increasing the length of the acousticalchannel 413 between the transmitter 414 and receiver 415. This increasein the transit distance of the acoustical channel thus enables adetection and measurement of the applied force to be made in the mannerdescribed above.

The pressure deformable body 411 may be of rubber or other soundabsorbing material. In addition, the narrow sensor strip 413 couldextend for substantially the complete circumference of body 411, but thetransmitter should be spaced from the receiver, on the side opposite tothat of the sensor channel 413, by sound absorbing material so as tosubstantially confine the sonic waves to the sonic channel defined bythe elastomeric strip 413.

Sensor 410 illustrated in FIG. 41 may be used in many of theabove-described applications but is particularly useful in an apneamonitor, as illustrated in FIG. 43, to monitor both cardiac andrespiratory activity of a person.

FIG. 42 illustrates another sensor constructed in accordance with thepresent invention and particularly useful in an apnea monitor, asillustrated in FIG. 43. Thus, as shown in FIGS. 42 and 43, the sensor,therein generally designated 420, is mounted between a pair of plates421, 422, which may be applied over, under, or within a mattressoccupied by a person (e.g., a baby, elderly patient, etc.) whose cardiacactivity and respiratory activity are to be monitored. Sensor 420includes a printed circuit board 423 formed with an opening 423 astraddled by a pair of electrical-conductive pads 424. Anacoustical-channel type sensor including a strip of elastomeric material425 having a sonic transmitter 426 at one end and a sonic receiver 427at the opposite end, is applied over the electrically-conductive pads424 to overlie the opening 423 a in the printed circuit board 423. Theelectrical connections to the sonic transmitter and sonic receiver areconnected by solder 428, to the conductive pads 424.

The printed circuit board 423, with the elastomeric acoustical channel425 secured thereto, is supported on a body of rubber or other soundabsorbing material, having a projection 429 a projecting through opening423 a in the printed circuit board so as to support the underface of theelastomeric strip 425. The printed circuit board 423 further includes arigid cap 430 overlying the sonic transmitter and sonic receiver of theelastomeric strip 425 and formed with a central opening 430 a exposingthe upper side of the elastomeric strip 425. Another body of rubber orother sound absorbing material 431 is interposed between cap 430 and theother panel 421, and is formed with a projection 431 a projectingthrough the opening 430 a in cap 430 to engage the upper side of theelastomeric strip 425.

It will thus be seen that any force applied to plate 421 will deflectthe elastomeric strip 425, as shown in broken lines in FIG. 42, tothereby increase the effective length of the elastomeric strip, andthereby the transit time of a sonic wave from its transmitter 426 to itsreceiver 427, such as to provide a measurement of the applied force inthe manner described above.

As indicated above, sensor 420 of FIG. 42 (as well as sensor 410 of FIG.41), particularly when included in an apnea monitor as illustrated inFIG. 43, is so sensitive to applied forces as to be able to detect notonly respiratory activity and other motions by the person, but alsoheart activity of the person. Thus, as shown in FIG. 43, the output ofsensor 420 can be applied to a control circuit 432, which can therebydetect both the lack of respiratory activity, as shown by block 433, orthe lack of heart activity, as shown by block 434.

The illustrated apnea monitor thus includes a vibrator 435, which isactuated when necessary to stimulate the person, and an alarm 436 whichmay be actuated to notify another of an alarm condition. Thus, as shownin FIG. 43, if no heart activity is detected for a predetermined periodof time (t₁, e.g., five seconds), alarm 436 is immediately actuated. Onthe other hand, if no respiratory activity is detected for apredetermined interval (t₂, e.g., twenty seconds), vibrator 435 isactuated in an attempt to stimulate the person; and if the lack ofrespiratory activity continues for another time interval (t₃, e.g., anadditional ten seconds), the alarm 436 is actuated.

It will be appreciated that such an apnea monitor could be provided fora single person, (e.g., baby, elderly patient); on the other hand, wheretwo persons (e.g., elderly persons) occupy a double bed, two such apneamonitors could be provided, one for each person, so as to actuate analarm to alert the other person whenever an alarm condition is found tobe present.

It will be appreciated that the sensor illustrated in FIG. 42, as wellas the apnea monitor illustrated in FIG. 43, may be used in many otherapplications, e.g., in the bed sore preventing apparatus or in theanti-snoring apparatus, described earlier.

Because of the extremely high sensitivity attainable by the sensors ofthe present invention in detecting and measuring extremely smalldisplacements or micro-displacements, such sensors are particularlyuseful for synchronizing the operation of imaging systems in accordancewith the respiratory and/or cardiac activity of the patient.

Thus, the detailed images produced by magnetic resonance imaging (MRI)systems are often blurred by the motion of the patient during cardiacand respiratory cycles. The patient's ECG signals are frequently used asgating signals for synchronizing the operation of the MRI apparatus, butECG signals do not closely correlate with the mechanical motion causingthe blurring. Finger probes have also been used for this purpose fordetecting pulsatile blood flow, but the use of such sensors alsointroduces a time delay between the motions caused by the heart activityand the sensing of the blood pulse.

Sensors constructed in accordance with the present invention areparticularly useful for directly sensing extremely small displacementsarising from cardiac activity and/or respiratory activity in order toproduce gating signals synchronizing the operation of the MRI apparatusin accordance with such detected movements, and thereby to minimize oreliminate blurring of the images produced by such movements. Forexample, an acceleration-type sensor as described above may be appliedto the person's chest to detect cardiac activity; and/or a displacementtype sensor as described above may be applied against the patient'schest, as by an elastic belt, or under the patient's body supportingmember, for detecting respiration activity of the patient. By using suchsensors for detecting micro-displacements of the patient arising fromcardiac and/or respiratory activity and for producing gating signals forsynchronizing the operation of the MRI apparatus, the blurring producedby body motion during an imaging operation can be minimized oreliminated to produce much clearer images than those heretoforeattainable by ECG or pulsatile blood signals.

While sensors constructed in accordance with the invention are thusparticularly useful for MRI procedures, they are also useful in othertypes of imaging, including CT, PET, nuclear, ultrasonic, and X-rayimaging.

In addition, while such sensors are particularly useful for detectingheart and respiration activity, and for synchronizing the operation ofthe imaging system in accordance with such detected activity, it will beappreciated that such sensors could also be used for detecting otheractivities of the patient, such as stomach movements, stone movements ina kidney, etc. and used for synchronizing the operation of the imagingsystem in accordance therewith.

FIGS. 44-50 illustrated further features useful with respect to thesensors and systems utilizing such sensors described above. Thus FIGS.44 and 45 relate to a novel frequency-measurement circuit and method;FIGS. 46-48 relate to a novel temperature-compensation circuit andmethod; and FIGS. 49 and 50 relate to a novel frequency-generationcircuit and method.

With respect to the frequency measurement circuits of FIGS. 44 and 45,the conventional method to measure time intervals with high resolutionis to use high frequency clock oscillators. However, conventionaloscillators are expensive and have large current consumption, whichdetract from their use in low power and low cost applications of theabove-described sensor system.

In the method of FIG. 2, assume the frequency f_(x) in a feed back loopis 1 MHz (i.e., period is 1 μsec); the measuring time is 10 msec; andthe clock frequency is 100 MHz (i.e., clock period or resolution is 10nsec). Actually, a duration of 10 msec/1 μsec (10,000 periods) ismeasured, enabling distinguishing changes in a total duration of 1 nsec,or in a period of 1 nsec (10,000=10⁻⁴ nsec), i.e., differences betweenperiods of 10 μsec and 0.9999999 μsec will be distinguishable. Thiscorresponds to a frequency difference of 0.1 Hz for 1 MHz. Such a systempermits very high resolution, but a 100 MHz clock results in thedisadvantages described above.

Now consider the same measurement conditions, i.e., a measured frequencyof 1 MHz, a deviation of 0.1 Hz, and a measuring time of 10 msec. FIG.44 illustrates a measurement circuit for this purpose, which consists offollowed units: a reference frequency synthesizer 441; a frequency mixer442; a clock oscillator 443; and a measuring unit 444.

Assume the synthesizer 441 produces a frequency f_(s)=999.5 kHz. Thus,the output of mixer will be 1 MHz-999.5 kHz=500 Hz without deviation,and 1.0000001 MHz-999.5 kHz=500.1 Hz with 0.1 Hz deviation of themeasured frequency.

A frequency of 500 Hz corresponds to a period of 2 msec, and a frequencyof 500.1 Hz corresponds to 1.9996 msec. If a duration of 5 periods (10msec) is to be measured, and the difference 5·(2 msec-1.9996 msec), (or0.002 msec) is to be distinguished, a clock 383 m with this period(0.002 msec) is needed, which corresponds to a frequency of 500 kHz.

Thus it is possible to use a low frequency clock 443 (e.g., 500 Khz)instead of a 100 MHz clock, to provide the same resolution. On the otherhand, the clock may be increased, (e.g., up to the relative low value of5 MHz) to reduce the measuring time (e.g., to 1 msec).

FIG. 45 illustrates a manner in which the frequency meter and the clockoscillator may be realized in a microprocessor 450 with a capturefeature, i.e., each edge of measured frequency may control the internallatch register in order to fix the state of the internal counter whichis clocked with the internal clock oscillator. The processor calculatesall the time difference between successive stages of the latch register.

The synthesizer (451, FIG. 45) may be realized as a counter 451 of theclock oscillator output pulses, and its frequency may be controlled witha preset signal from the microprocessor. The mixer (452, FIG. 45) may berealized as the digital AND-logic element 452 with a low pass analogfilter 453 and comparator 454. Like any non-linear unit, the AND-logicelement 452 creates difference and summation frequencies on its output.The low pass filter 453 extracts just the difference sinusoidalfrequency, The comparator 454 creates square pulses which are receivedwith the frequency meter 444 (FIG. 44).

With respect to FIGS. 46-48 illustrating the temperature compensationfeature, the temperature influences the speed of energy propagation andinitiates thermal expansion which, as noted above, results in changes ofthe transit time between the transmitter and the receiver. Because ofthe very high sensitivity of the above-described sensor systems, theremay be considerable temperature drift in the output frequency. When onemeasures the signals which changes slowly, it is very difficult todistinguish between a signal change and a temperature drift.

Temperature drift may be eliminated by a two-channel measurement asdescribed above with respect to FIGS. 16 and 44. FIG. 46 illustratessuch a two-channel measurement system including the two sensors S₁, S₂to measure force. As shown in FIG. 46, the force to be measured acts toexpand one sensor S₁ and to contract sensor S₂. Thus the outputfrequency of sensor S₂ will be increased (+Δf) and that of sensor S₁will be decreased (−Δf). The final output signal is developed bysubtracting one output frequency from the other:F=f ₁ f ₂=(f ₀ +Δf+Δf _(T))−(f ₀ −Δf+Δf _(T))=2ΔfSince the temperature drift results in the same changes (Δf_(T)) in bothchannels, the subtraction will eliminate changes caused by temperaturedrift.

Actually in the standard method as shown in FIG. 47, each measuringchannel 471, 472 measures the ratio of the input frequency and theclock. The standard method uses a special clock oscillator 473 for bothmeasuring channels and for the processor 474. A disadvantage of theabove-described method, therefore, is that it needs to use two separatemeasuring channels, and to allocate processor time to perform thesubtraction algorithm.

FIG. 48 illustrates an improved method in which one sensor S₁ is usedfor the single measuring channel, and the second sensor S₂ is connectedto the input of a phase-locked loop (PLL) circuit 481. The highfrequency output of the PLL circuit 481 is used as the clock of both themeasuring channel 482 and the processor 483. When the temperaturechanges, the frequencies of the measuring channel and the clock arechanged proportionally. Thus its ratio is not changed since the appliedforce produces opposite changes of frequencies, and thereby oppositechanges in the above ratio:

$R = {\frac{Fchannel}{Fcloc} = {\frac{f_{0} + {\Delta\; f} + {\Delta\; f_{T}}}{f_{0} - {\Delta\; f} + {\Delta\; f_{T}}} \approx {1 + \frac{2\;\Delta\; f}{f_{0}}}}}$It is to be noted that the ratio need not be calculated in theprocessing unit; rather it is automatically reflected in the output ofthe measuring channel.

As indicated above, this technique also enables the construction of anew frequency-generator. It is to be noted that crystal oscillators usedin existing frequency generators usually consist of a single quartzcrystal with two electrodes which are connected to an electricalfeed-back circuit. The oscillation frequency is determined by themechanical resonance of the crystal, which is much more stable than theresonance frequency of electrical circuits with capacitance andinductance. A disadvantage of such oscillators is that the crystaloperates simultaneously as an electromechanical transducer and as amechanical resonator. It is very difficult to combine differentrequirements in one material, e.g., high electromechanical coupling of atransducer, and temperature stability of a resonator. Regardless of thefact that quartz is considered as a very good material for oscillators,for many applications its temperature stability is not sufficient.

The novel sensors described above are capable of providing a frequencygenerator having very high temperature stability since frequency ofoscillation depends on the properties and geometry of the channelmaterial rather than of the piezo-transmitter and receiver. Thus it ispossible to choose the most suitable materials separately for themechanical resonator and for the electromechanical transducers.

Suppose a system includes two acoustical channels as described abovewith each channel having a transmitter and a receiver controlling thetransmitter to transmit an integer member of sonic waves to thereceiver, and with electrical feedback. Each channel is produced frommaterial having a low coefficient of linear expansion, which coefficientdiffer slightly in the two channels. Consequently, when the temperaturechanges, the integer number of sonic waves in each channel, and therebythe frequency of each channel, will be changed. As shown in FIG. 45,there is a certain temperature point where the channel frequencies areequal and where changes in temperature produce opposite changes infrequency.

FIG. 50 illustrates such a system including the two channels 501, 502and their feedbacks 503, 504, but provided with an additional feedbackconsisting of a phase detector 505 with a low pass filter, and a controldevice 506. The inputs of the phase detector 505 are the outputs of thetwo channels 501, 502. The output of the control device 506 forces bothchannels to change their lengths identically and simultaneously.

At a certain temperature point, when the frequencies are equal, theoutput of the phase detector 505 is zero, and the control device 506does not influence the channel. When the temperature is changed, bothfrequencies attempt to change. This will immediately produce adifference of phases in the outputs of the two channels because of theslightly different temperature sensitivity of the channels. The outputsignal applied by the phase detector 505 to the control device 506 willforce the channels to change length in such manner to equalize both ofthe frequencies. Thus both frequencies will return to the stabilizationpoint.

Control device 506 may be implemented in different forms including thefollowing:

1. It may be embodied in a heating device. In this case a stabletemperature point is chosen higher than the maximum working temperature.Thus when the environmental temperature is changed, the temperature ofboth channels is kept at a point where the frequencies are equal; i.e.,the above-mentioned additional feedback is actually athermo-stabilization device.

2. It may be embodied in an electromechanical actuator. In this case,the control device will produce an expansion or contraction of bothchannels with the ratio corresponding to their temperature coefficients.Thus, when the environmental temperature is changed, the length of bothchannels is kept at a point where the frequencies are equal.

Such an actuator may be implemented in different forms: as apiezo-electric actuator, which changes its length according to thereverse piezoelectric effect when voltage is applied on its electrodes;as a magnetostrictive actuator, which changes its length according tothe magnetostriction effect when electrical current flows in its coil;or as any other actuator, which produces a displacement according to itselectrical input.

While the above-described features as illustrated in FIGS. 44-50 areparticularly useful with respect to sensors and systems constructed inaccordance with the present invention as illustrated in FIGS. 1-43, itwill be appreciated that such features are also useful in otherapplications where frequency-measurement, temperature compensation,and/or frequency generation is also involved.

Also, while the invention has been described with respect to variouspreferred embodiments, it will be appreciated that these are set forthmerely for purposes of example, and that many other variations andapplications of the invention may be made. For example, a sensorassembly may include not only one of the above-describedaxially-extending sensors (e.g., FIGS. 1-9), transversely-extendingsensors (e.g., FIGS. 34-36 and 42), or circumferentially-extendingsensors (e.g., FIG. 41), for detecting changes in the transit distanceof the acoustical channel in response to the condition being detected,but may also include a temperature-sensitive element, such as shown inFIG. 8, which changes the transit velocity of the acoustical wave inresponse to the condition being detected. In addition, while thepreferred embodiments of the invention described above utilize sonictransmitters and receivers, it will be appreciated that the sensor couldalso be implemented with transmitters and receivers of visible light,infrared, RF or other electromagnetic energy.

Many other variations, modifications and applications of the inventionwill be apparent.

1. Apparatus for measuring a predetermined parameter having a known ordeterminable relationship with respect to the transit time of an energywave through a medium, comprising: a sensor for sensing saidpredetermined parameter, said sensor including a transmitter fortransmitting energy waves through said medium and a receiver forreceiving said energy waves transmitted by said transmitter; and a dataprocessor for measuring the transit time, or changes in the transittime, of energy waves from said transmitter to said receiver to therebyproduce a measurement of said predetermined parameter; characterized inthat said sensor includes a body of soft elastomeric material havinghigh transmissivity and low attenuation properties with respect to saidenergy waves, said transmitter and receiver being embedded in spacedrelation to each other in said body of soft elastomeric material todefine a transmission channel constituted of the elastomeric materialbetween said transmitter and reciever, such that said parameter, whensensed by said sensor, produces a displacement of said transmitterrelative to said receiver, whereby measuring the transit time, orchanges in the transit time, of said energy waves through saidtransmission channel from said transmitter to said receiver provides ameasurement of the displacement of the transmitter relative to thereceiver, and thereby of said predetermined parameter.
 2. The apparatusaccording to claim 1, wherein said elastomeric material is a siliconeelastomer.
 3. The apparatus according to claim 1, wherein saidelastomeric material has a Shore A hardness of 5-60.
 4. The apparatusaccording to claim 1, wherein said elastomeric material has a Shore Ahardness of 7-20.
 5. The apparatus according to claim 1, wherein saidenergy wave is a sonic wave.
 6. The apparatus according to claim 1,wherein the apparatus includes two of said sensors mounted on a commonsupport with one of their ends facing and aligned with each other, andtheir opposite ends fixed to said support; said facing ends of thesensors being fixed to a member located between them and displaceable bysaid predetermined parameter towards one sensor and away from the othersensor, such that the displacement of said displaceable member in eitherdirection compresses the elastomeric body of one sensor and expands theelastomeric body of the other sensor, thereby substantially eliminatingtemperature and other transient influences, while enhancing themeasurement of said predetermined parameter.
 7. A sensor for sensing apredetermined parameter having a known or determinable relationship withrespect to the transit time of an energy wave through a medium,comprising: a body of soft elastomeric material having hightransmissivity and low attenuation properties with respect to saidenergy waves; and a transmitter and receiver carried by said body inspaced relation to each other to define an acoustical transmissionchannel constituted of the elastomeric material between said transmitterand receiver, such that the energy waves received by said receiver arethose transmitted by said transmitter through said acousticaltransmission channel after having traversed at least a portion of saidbody of soft elastomeric material.
 8. The sensor according to claim 7,wherein said elastomeric material is a silicone elastomer.
 9. The sensoraccording to claim 7, wherein said elastomeric material has a Shore Ahardness of 5-40.
 10. The sensor according to claim 7, wherein saidelastomeric material has a Shore A hardness of 7-20.
 11. The sensoraccording to claim 7, wherein said energy wave is a sonic wave.
 12. Thesensor according to claim 7, wherein said transmitter and receiver areembedded in said body of elastomeric material.
 13. The sensor accordingto claim 7, wherein said body of elastomeric material includes an arrayof said transmitters and receivers for use as a keyboard orpressure-distribution sensor.
 14. The sensor according to claim 7,wherein said body of elastomeric material is of annular shape forreceiving a finger, wrist or arm of a person.
 15. The sensor accordingto claim 7, wherein said sensor also includes a weight which acts as aninertia member effective to make the sensor sensitive to the rate ofchange of the spacing between said transmitter and receiver.
 16. Thesensor according to claim 15, wherein said weight is carried by apivotably mounted arm.
 17. The sensor according to claim 7, wherein saidbody of soft elastomeric material is in the form of a narrow strip suchas to define a narrow transmission channel between said transmitter andreceiver.
 18. The sensor according to claim 17, wherein said energy waveis a sonic wave and said narrow transmission channel is a narrowacoustical channel.
 19. The sensor according to claim 18, wherein saidsensor further includes a damper material having high sonic-waveattenuation properties at the opposite ends of said strip of softelastomeric material, said damper material being effective to absorbsonic waves except those in said narrow acoustical channel. 20.Apparatus according to claim 1, wherein said apparatus is in the form ofa hand-held portable electrical device comprising a housing carryingsaid sensor for enabling the device also to be used for measuring saidpredetermined parameter.
 21. The apparatus according to claim 20,wherein said hand-held device is a cellular telephone handset orportable digital assistant.
 22. Apparatus according to claim 1, whereinsaid data processor includes a frequency measuring circuit, comprising:a frequency synthesizer generating a predetermined frequency; a mixerhaving one input receiving said predetermined frequency of thesynthesizer, and a second input receiving the frequency of transmissionby said transmitter of the sensor, and for producing an output frequencyin which the frequency of one input is subtracted from that of the otherinput; a clock oscillator for generating a clock frequency; and anoutput circuit having one input receiving the output of said mixer, anda second input receiving the output of said clock oscillator forproducing a measurement of the frequency of transmission by saidtransmitter of the sensor.
 23. Apparatus according to claim 6, whereinsaid data processor includes: a single measuring channel having an inputfrom one sensor and an output to a CPU; and a phase-locked loop havingan input from the other sensor, and an output providing clock pulses tosaid single measuring channel and to said CPU.
 24. A system forgenerating a predetermined frequency, comprising: first apparatusaccording to claim 1 including a first body of soft elastomeric materialdefining a first acoustical channel of a first effective length andhaving a first coefficient of linear expansion in response totemperature; a second apparatus according to claim 1 including a secondbody of soft elastomeric material defining a second acoustical channelof a second effective length and having a second coefficient of linearexpansion in response to temperature different from said firstcoefficient of linear expansion; a first electrical feedback circuitfrom said first apparatus for controlling the frequency thereof; asecond electrical feedback circuit from said second apparatus forcontroling the frequency thereof; a phase detector with a low passfilter receiving the outputs of said first and second electricalfeedback circuits; and a control device controlling said first andsecond bodies of soft elastomeric material in response to the output ofsaid phase detector to cause both bodies of soft elastomeric material tochange their effective lengths such as to equalize the frequencies ofboth acoustical channels.
 25. A system for generating a predeterminedfrequency, comprising: a first acoustical channel having a transmitterand a receiver controlling the transmitter to transmit an integer numberof sonic waves to the receiver, said first acoustical channel having afirst effective length and a first coefficient of linear expansion inresponse to temperature; a second acoustical channel having atransmitter and a receiver controlling the transmitter to transmit aninteger number of sonic waves to the receiver, said second acousticalchannel having a second effective length and a second coefficient oflinear expansion in response to temperature; a first electrical feedbackcircuit from said first acoustical channel to control the frequencythereof a second electrical feedback circuit from said second acousticalchannel to control the frequency thereof; a phase detector receiving theoutputs of said first and second electrical feedback circuits; and acontrol device controlling said first and second acoustical channels inresponse to the output of said phase detector to equalize thefrequencies of the two acoustical channels.
 26. The system according toclaim 25, wherein said phase detector has a low-pass filter.
 27. Thesystem according to claim 25, wherein each of said acoustical channelsincludes a body of soft elastomeric material having high sonic-wavetransmissivity and low sonic-wave attenuation.